When a simulated clock tick happens, other
potential sources of external events are polled to determine if data
has arrived. These include console and/or other simulated multiplexer
and network input. So, the console and any other configured
multiplexer devices will be polled 100 times a second.

It might just happen to not work well with NetBSD cpu stats sampling, or
there might be a bug - I haven't investigated more closely. top shows
one cpu 100% busy, but that may be a missampling.
Anyway, I just wondered why it did not use blocking io and threads, and you
answered that - looking forward to newer versions.